The invention relates to a liftgate assembly having force assist struts. More specifically, the invention relates to a liftgate assembly having adjustable force assist struts.
Liftgates for motor vehicles require counterbalancing. The counterbalance allows the operator thereof to lift the liftgate with a minimal of effort. Further, the counterbalance prevents the liftgate from falling after the liftgate has been opened. This avoids injury to the operator as the liftgate will not fall on him or her.
Struts are usually used as the counterbalance for the liftgate. The struts are pneumatic cylinders typically filled with a gas material. A rod extends out from the pneumatic cylinder whereas the pressure created by the gas within the pneumatic cylinder provides a force assist for two purposes.
The first purpose is to aid the user in lifting the liftgate to its open position. The liftgate, including a large windowpane, is heavy and many users of the liftgate would be challenged to fully open the liftgate. The struts utilize the gas pressure to force the liftgate upwardly to assist the user in raising the liftgate.
The second purpose for using struts is for maintaining the liftgate in an open position without requiring a latch or support member that needs to be released when closing the liftgate. The struts allow the users to access the cargo area easily without much effort.
A liftgate is normally over-counterbalanced to auto open beyond a neutral force zone at the closure position. When a liftgate latch releases, the user urges the liftgate through the neutral zone until the counterbalance acts to swing the liftgate fully open. And in closing the liftgate, the user must first pull down and then change hand position to push in overcoming the counterbalance bias.
There are disadvantages to using the struts for providing force assist for the liftgate. In many instances, the liftgate is raised by the struts to a position that is unreachable to those users who are not able to reach up to the fully open liftgate. These users must either tie tethers to the liftgate or find objects to step up to reach the fully open liftgate.
Another disadvantage to the strut lift assist is that there is little regulation as to the fully open position. The finish of the liftgate may be damaged when the liftgate is opened in a low clearance area, e.g., under an open garage door. If opening the liftgate in a low clearance area is done routinely, adjustment to the fully open position may be desirable.
Yet another disadvantage associated with the current arrangement of using struts to assist in forcing the liftgate to an open position is that it is temperature dependent. Because the gas pressure in the strut obeys the characteristics of an ideal gas, the strut""s force is significantly dependent on ambient temperature. As the ambient temperature rises, so too does the temperature of the gas within the pneumatic cylinder of the strut. This increases the force that the strut is able to generate resulting in a liftgate that rises quickly and is more difficult to close. Likewise, as ambient temperature decreases, so too does the force that the strut is able to produce. This reduction of force may result in little or no force assisting requiring the user to provide a force equal to the weight of the liftgate and windowpane to open the liftgate.
According to one aspect of the invention, there is provided a liftgate force control assembly that adjusts the force required to move a liftgate that is pivotally secured to a motor vehicle. The liftgate force control assembly includes a track that is fixedly secured to the motor vehicle. A follower is movably secured to the track. A strut defines a moving end and a secured end. The secured end is pivotally secured to the liftgate and the moving end is pivotally secured to the follower. The strut defines a moment with respect to the hinge that secures the liftgate to the motor vehicle. A motor is connected to the follower. The motor moves the follower along the track changing the moment of the strut such that the force required to move the liftgate changes as the moment changes.
According to another aspect of the invention, there is provided a vehicle having a liftgate mounted thereon by hinges. The liftgate is pivotally movable to open and close an opening in the vehicle. A pair of struts is operably connected between the liftgate and the vehicle to effect a lifting force on the liftgate. Each of the struts is pivotally mounted at one end to one of the liftgate and the vehicle and slidably mounted for reciprocating movement at an opposite end to the other of the liftgate and the vehicle. The reciprocating movement changes a magnitude of the lifting force being transferred to the liftgate. A drive motor operably engages the slidable end of each of the struts and operable to effect the reciprocating movement.